--- a/basicdatatype.rst Thu Sep 23 11:26:34 2010 +0530
+++ b/basicdatatype.rst Thu Sep 23 12:29:30 2010 +0530
@@ -10,15 +10,10 @@
* Operators with a little hands-on on how they can be applied to
the different data types.
-Since this a hands on session, you will require python installed in your
-computer.
-.. #[Nishanth]: this line is not required
+
First we will explore python data structures in the domain of numbers.
-There are three built-in data structures in python to represent numbers.
-
-.. #[Nishanth]: Did you mean data types when you said data structures??
- Data structures is used for lists and others.
+There are three built-in data types in python to represent numbers.
{{{ A slide to make a memory note of this }}}
@@ -31,12 +26,12 @@
Lets first talk about integers. ::
a = 13
+ a
-.. #[Nishanth]: give a space before and after the = sign
Thats it, there we have our first integer variable a.
-.. #[Nishanth]: Show the value of a
+
If we now see ::
@@ -49,7 +44,7 @@
a.<Tab>
-.. #[Nishanth]: a.<Tab> is not a good idea for int or float
+
Lets see the limits of this int.
@@ -81,21 +76,16 @@
format. There is always an aproximationation. This is why we should
never rely on equality of floating point numbers in a program.
-The last data structure in the list is complex number ::
+The last data type in the list is complex number ::
c = 3.2+4.6j
as simple as that so essentialy its just a combination of two floats the
-imaginary part being define by j notation usually used in electrical
-engineering. Complex numbers have a lot of functions specific to them.
+imaginary part being define by j notation instead of i. Complex numbers have a lot of functions specific to them.
Lets check these ::
c.<Tab>
-.. #[Nishanth]: rephrase the "j used in electrical engineering"
- Its ok if you skip it also. Just say that here
- j is used and not i
-
Lets try some of them ::
c.real
@@ -118,14 +108,13 @@
You can apply different Boolean operations on t now for example ::
f = not t
- In[]: f
- In[]: f or t
- In[]: f and t
+ f
+ f or t
+ f and t
-.. #[Nishanth]: remove In[]: and include spaces before and after = symbol
- I don't want to edit it everywhere in the script
+
-The results explanotary in themselves.
+The results are explanotary in themselves.
The usage of boolean brings us to an interesting question of precendence.
What if you want to apply one operator before another.
@@ -143,13 +132,13 @@
one ::
- In[]: (a and b) or c
+ (a and b) or c
This expression gives the value True
where as the expression ::
- In[]: a and (b or c)
+ a and (b or c)
gives the value False.
@@ -170,9 +159,10 @@
We create our first list by typing ::
- In[]: num = [1, 2, 3, 4]
+ num_list = [1, 2, 3, 4]
+ num_list
-.. #[Nishanth]: Show the value of the variable
+
Items enclosed in square brackets separated by comma
constitutes a list.
@@ -180,19 +170,19 @@
We can have a list something like ::
- In[]: var = [1, 1.2, [1,2]]
+ var_list = [1, 1.2, [1,2]]
+ var_list
-.. #[Nishanth]: Show the value of the variable
-print var
+
Now we will have a look at strings
type ::
- In[]: w="hello"
+ In[]: greeting_string="hello"
-.. #[Nishanth]: Show the value of the variable
-w is now a string variable with the value "hello"
+
+greeting_string is now a string variable with the value "hello"
{{{ Memory Aid Slide }}}
@@ -212,7 +202,7 @@
To create a tuple we use normal brackets '('
unlike '[' for lists.::
- In[]: t = (1, 2, 3, 4, 5, 6, 7, 8)
+ In[]: num_tuple = (1, 2, 3, 4, 5, 6, 7, 8)
Because of their sequential property there are certain functions and
operations we can apply to all of them.
@@ -223,53 +213,54 @@
They can be accessed using index numbers ::
- In[]: num[2]
- In[]: num[-1]
- In[]: w[1]
- In[]: w[3]
- In[]: w[-2]
- In[]: t[2]
- In[]: t[-3]
+ In[]: num_list[2]
+ In[]: num_list[-1]
+ In[]: greeting_string[1]
+ In[]: greeting_string[3]
+ In[]: greeting_string[-2]
+ In[]: num_tuple[2]
+ In[]: num_tuple[-3]
-Negative indices can be used to access in reverse
-.. #[Nishanth]: Elaborate on indexing.
- Indexing starts from 0 when moving from left to right
- Indexing starts from -1 when moving from right to left
+Indexing starts from 0 from left to right and from -1 when accessing
+lists in reverse. Thus num_list[2] refers to the third element 3.
+and greetings [-2] is the second element from the end , that is 'l'.
+
+
Addition gives a new sequence containing both sequences ::
- In[]: num+var
- In[]: p="another string"
- In[]: w+p
+ In[]: num_list+var_list
+ In[]: a_string="another string"
+ In[]: greeting_string+a_string
In[]: t2=(3,4,6,7)
- In[]: t+t2
+ In[]: num_tuple+t2
len function gives the length ::
- In[]: len(num)
- In[]: len(w)
- In[]: len(t)
+ In[]: len(num_list)
+ In[]: len(greeting_string)
+ In[]: len(num_tuple)
Prints the length the variable.
We can check the containership of an element using the 'in' keyword ::
- In[]: 3 in num
- In[]: 'H' in w
- In[]: 2 in t
+ In[]: 3 in num_list
+ In[]: 'H' in greeting_string
+ In[]: 2 in num_tuple
We see that it gives True and False accordingly.
Find maximum using max function and minimum using min::
- In[]: max(t)
- In[]: min(w)
+ In[]: max(num_tuple)
+ In[]: min(greeting_string)
Get a sorted list and reversed list using sorted and reversed function ::
- In[]: sorted(num)
- In[]: reversed(w)
+ In[]: sorted(num_list)
+ In[]: reversed(greeting_string)
As a consequence of the order one we access a group of elements together.
This is called slicing and striding.
@@ -287,8 +278,8 @@
In[]: j[1:4]
The syntax for slicing is sequence variable name square bracket
-first element index, colon, second element index.::
-.. #[nishanth]: specify that the last element is not included
+first element index, colon, second element index.The last element however is notincluded in the resultant list::
+
In[]: j[:4]
@@ -305,9 +296,9 @@
Lets see by example ::
- In[]: z=[1,2,3,4,5,6,7,8,9,10]
- In[]: z[1:8:2]
- Out[]:[2, 4, 6, 8]
+ new_num_list=[1,2,3,4,5,6,7,8,9,10]
+ new_num_list[1:8:2]
+ [2, 4, 6, 8]
The colon two added in the end signifies all the alternate elements. This is why we call this concept
striding because we move through the list with a particular stride or step. The step in this example
@@ -316,62 +307,54 @@
We have talked about many similar features of lists, strings and tuples. But there are many important
features in lists that differ from strings and tuples. Lets see this by example.::
- In[]: z[1]=9
- In[]: w[1]='k'
+ In[]: new_num_list[1]=9
+ In[]: greeting_string[1]='k'
{{{ slide to show the error }}}
-.. #[Nishanth]: Use sensible variable names. At this point no one will remember
- that z is a list and w is tuple.
- for example you can use names like some_list, a_tuple etc.
- or you can also use l for list, t for tuple and s for string
+
As you can see while the first command executes with out a problem there is an error on the second one.
Now lets try ::
- In[]: t[1]=5
+ In[]: new_tuple[1]=5
Its the same error. This is because strings and tuples share the property of being immutable.
We cannot change the value at a particular index just by assigning a new value at that position.
-In case of strings we have special functions to appy relacement and other things while tuples cannot
-be changed at all.
-
-.. #[Nishanth]: Even in strings also the special functions do not modify the
- original string. A new string is created instead. These have
- been provided for string manipulation.
- hence I don't think you have to mention this.
We have looked at different types but we need to convert one data type into another. Well lets one
by one go through methods by which we can convert one data type to other:
We can convert all the number data types to one another ::
- In[]: i=34
- In[]: d=float(i)
+ i=34
+ d=float(i)
+ d
Python has built in functions int, float and complex to convert one number type
data structure to another.
- In[]: dec=2.34
- In[]: dec_con=int(dec)
-
-.. #[Nishanth]: Show the value of the variables
+ dec=2.34
+ dec_con=int(dec)
+ dec_con
+
As you can see the decimal part of the number is simply stripped to get the integer.::
- In[]: com=2.3+4.2j
- In[]: float(com)
+ com=2.3+4.2j
+ float(com)
+ com
In case of complex number to floating point only the real value of complex number is taken.
Similarly we can convert list to tuple and tuple to list ::
- In[]: lst=[3,4,5,6]
- In[]: tup=tuple(lst)
- In[]: tupl=(3,23,4,56)
- In[]: lst=list(tuple)
+ lst=[3,4,5,6]
+ tup=tuple(lst)
+ tupl=(3,23,4,56)
+ lst=list(tuple)
However string to list and list to string is an interesting problem.
Lets say we have a string ::
@@ -379,7 +362,6 @@
In: somestring="Is there a way to split on these spaces."
In: somestring.split()
-.. #[Nishanth]: Did you try list(somestring). What does it give??
This produces a list with the string split at whitespace.
similarly we can split on some other character.